Leek and Cauliflower Soup

This is my mother's recipe. It's super easy to make, but it's one of the most satisfying soups you'll ever taste. There's something about the wonderful cauliflower texture and the delicate leek-onion flavor. Just a match made in heaven!
1 cauliflower
3 leeks
1/4 C butter
2 C vegetable stock (or more as needed)
1 C milk
salt and pepper to taste
Cheddar cheese, grated (optional)

Wash and trim the cauliflower into florets, removing all the green leaves and the tough woody core.
Then wash and slice the leeks.
Melt the butter in a medium sized pan and coat the cauliflower and the leeks. Season with a little salt and pepper and cook the vegetables very gently on a low heat for about 15 minutes.
When they are al dente add the stock and milk, and increase the heat and cook for about 10 more minutes until the vegetables are cooked. 
Blitz the mixture with a stick blender until you have the desired consistency.
Serve hot with a little grated Cheddar cheese and some wholegrain bread. Delicious!